When voltage is applied between two electrodes of the organic electroluminescence device, holes are injected into the organic material layer at the anode and electrons are injected into the organic material layer at the cathode, the injected holes and electrons meet each other to form an exciton, and when the formed exciton falls down to a bottom state, light is emitted. Materials used as the organic material layer may be classified into a light-emitting material, a hole injection material, a hole transporting material, an electron transporting material, an electron injection material, and the like according to the function.
The light-emitting materials may be divided into blue, green, and red light-emitting materials according to the light-emitting color, and into yellow and orange light-emitting materials required for implementing a much better natural color. Further, a host/dopant system may be used as a light-emitting material in order to enhance color purity and light-emitting efficiency through an energy transfer.
Dopant materials may be divided into a fluorescent dopant using an organic material and a phosphorescent dopant in which a metal complex compound including heavy atoms such as Ir and Pt is used. Since the development of the phosphorescent dopant may theoretically enhance light-emitting efficiency by up to 4 times compared to the development of the fluorescent dopant, studies on not only phosphorescent dopants, but also phosphorescent hosts have been conducted.
As the hole transporting material, the hole injection material, the electron transporting layer, and the like, NPB, BCP, Alq3 and the like have been widely known until now, and as the light-emitting material, anthracene derivatives have been used. In particular, in the light-emitting material, metal complex compounds including Ir and having a great advantage in terms of enhancing the efficiency, such as Firpic, Ir(ppy)3 and (acac)Ir(btp)2, are used as blue, green and red phosphorescent dopant materials, and CBP is used as a phosphorescent host material.
However, since light-emitting materials in the related art have good light-emitting characteristics, but have low glass transition temperature, and thus poor thermal stability, these materials fall short of a level that sufficiently satisfies the lifespan of the organic electroluminescence device.